Various semiconductor devices such as, for example, gallium nitride (GaN) blue, green, and UV light emitting diodes (LEDs) and laser diodes (LDs) have been developed. Various Si/SiGe devices have also been developed.
Arrangements that can utilize a Sapphire wafer are described in the following U.S. Patent Application Publications, all of which are incorporated in their entirety herein by reference: U.S. Patent Application Publication Nos. 2009/0140296, 2009/0206368, 2009/0220047, and 2010/0027746, each of which is to Park et al. As discussed in the above-identified Park '047 patent application, since the invention of the first transistor in 1947, the microelectronics industry has used a diamond structured group IV semiconductor crystal such as silicon (Si) and germanium (Ge). Another cubic compound semiconductor crystal structure, i.e. zinc-blende-alpha structure with group III-V and group II-VI, was also utilized by the semiconductor industry for the last 30 years. In the early 1990s, new semiconductor materials having different crystal structures were introduced in the microelectronics industry. Examples of such materials include gallium nitride (GaN), aluminum nitride (AlN), and indium nitride (InN) in wurtzite structure. (See S. Nakamura, T. Mukai T, M. Senoh, Japanese Journal Of Applied Physics Part 2-Letters 30 (12a): L-1998-L2001 Dec. 1, 1991.)
The term “bandgap” generally refers to the energy difference between the top of the valence band and the bottom of the conduction band of a material; this is the energy gap that enables electrons to “jump” from one band to another. “Bandgap engineering” is the process of controlling or altering the bandgap of a material by controlling the composition of its constituent semiconductor alloys. “Bandgap energy” is a fundamental design parameter for semiconductor compositions, and has been particularly important in the design of heterojunction devices, as well as photoelectric devices such as laser diodes and solar cells.
The last 60 years of combined global effort in the field has resulted in a compilation of data showing bandgap energy as a function of the lattice constants associated with various semiconductor alloy compositions, for the diamond, zinc-blende and wurtzite structured materials referred to above. (See e.g., V. Swaminathan, A. T. Macrander, Materials Aspects of GaAs and InP Based Structures, published by Prentice-Hall, p. 25 (1991); O. Ambacher, Journal of Physics D-Applied Physics 31 (20): 2653-2710 Oct. 21, 1998.)
As discussed in the Park '047 publication, new semiconductor materials with rhombohedral super-hetero epitaxial structures in various combinations of cubic, trigonal and hexagonal crystalline structures have been developed.
U.S. Patent Application Publication No. 2009/0206368 to Park et al. discloses rhombohedral cubic semiconductor materials on a trigonal substrate with single crystal properties and devices based on such materials. As discussed in the Park '368 Patent Publication, Silicon Germanium (SiGe) on Sapphire is one approach to building Silicon Germanium On Insulator (SGOI) devices such as a high mobility transistor for K-band and higher frequency applications up to 116 GHz. Because Sapphire is one of the best insulators, the high-frequency parasitic capacitance between the semiconductor layer and the substrate can be essentially eliminated. Many epitaxial growths using this approach utilize Silicon On Sapphire (SOS) and Silicon Germanium On Sapphire (SGOS) technologies which take advantage of the rectangular R-plane of Sapphire aligned with the square-faced (001) plane or rectangle-faced (110) plane of the Si and Ge diamond structure. However, this approach often shows 90° rotated twin defects. Wafer bonding of SiGe on Sapphire has also been used. On the other hand, growth of cubic SiGe layers on the trigonal (0001) plane, i.e. C-plane of Sapphire has not been utilized for device fabrication so far due to the formation of 60° rotated twin defects.
SiGe is desirable as a material for transistors and other microelectronic devices, and SiGe can also be a good thermoelectric material that can be integrated into Si microelectronic circuits. Micro-coolers based on the super lattice of SiGe and SiGeC have shown substantial cooling power on the order of 1,000 Watt/cm2. A high thermoelectric figure of merit (ZT=S2σ/k) requires low thermal conductivity (k), high electrical conductivity (σ), and high Seebeck coefficient (S). While good semiconductor device materials require a single crystalline phase without defects, many good thermoelectric materials have electrically connected poly-type crystalline structures that scatter phonons, thus reducing thermal conductivity. For example, thermoelectric skutterudite material has three pnictogen square planes that can orient randomly. The growth of SiGe on the trigonal (0001) plane of Sapphire can scatter more phonons by utilizing the poly-type structures formed by twin crystals thus increasing the thermoelectric figure of merit by reducing thermal conductivity.
As also discussed in the Park '368 Patent Application Publication, despite these potential benefits, growing Silicon Germanium in the [111] direction on the trigonally structured C-plane (0001) Sapphire has been a challenge, because this atomic alignment allows poly-type crystalline structures with 60 degree-rotated twin defects as a result of stacking faults as well as twinning on the interface with the underlying trigonal substrate. The same considerations apply to cubic crystal structures of other group IV materials, as well as group III-V and II-VI materials, and alloys thereof.
X-ray diffraction methods to perform quality control of rhombohedral SiGe (C) on C-Sapphire have been developed as disclosed in U.S. Pat. Nos. 7,769,135 and 7,558,371, both to Park et al., each of which is incorporated in their entirety herein by reference. These X-ray diffraction methods permit measuring single crystal versus twin defect ratio in full wafer scale. Prior attempts to grow single crystalline Si, SiGe, SiGeC on C-Sapphire were generally not successful because it was not known how much single crystal was formed inside the epitaxial material without destroying the sample. Transmission Electron Microscopy (TEM) can “see” twin-defect in micrometer scale only (not full wafer scale), but the sample has to be destroyed to reveal the thin atomic layer.
Prior Silicone-on-Sapphire (SOS) technology typically utilizes R-plane (1-102) Sapphire which has a rectangular plane. Silicone (100) crystal is grown on R-plane sapphire. In contrast, the present invention utilizes C-plane (0001) Sapphire which has a triangle plane, and a Si (Ge) (C) (111) crystal is grown thereon.